In vehicles such as automobiles, an exhaust system of an engine employs an exhaust gas purification catalyst in order to purify exhaust gas containing air contaminants such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx). The exhaust gas purification catalyst is used to oxidize HC and CO for purification and reduce NOx for purification.
Such an exhaust gas purification catalyst is typically an exhaust gas purification catalytic material in which a catalytic metal such as Pd or Rh is loaded on the surface of a catalyst substrate of, for example, alumina with a high specific surface area or a CeZr-based composite oxide (complex oxide) having an oxygen storage/release capacity in a highly dispersed state. This exhaust gas purification catalyst is used for purifying exhaust gas.
Patent Document 1, for example, shows an exhaust gas purification catalyst including an Rh-containing upper catalyst layer and a Pd-containing lower catalyst layer on a catalyst substrate. In this exhaust gas purification catalyst, the upper catalyst layer includes CeZrNdM composite oxide particles containing Ce, Zr, Nd, and an alkali earth metal M and ZrLa-alumina particles in which ZrLa composite oxide containing Zr and La is loaded on the surface of alumina particles, and Rh is dispersed and loaded on the CeZrNdM composite oxide particles and the ZrLa-alumina particles.